First Hot Combustion Subsonic Retro Propulsion Tests in the Vertical Free Jet Facility Cologne (VMK)

Abstract

High uncertainties exist in modelling subsonic retro propulsion flow fields with CFD. For example, the choice of the turbulence model can greatly influence the flow field and the resulting heat loads. Hence, experiments with hot oxygen/hydrogen exhaust plumes and active counterflow are indispensable for the understanding of these flow fields. In the frame of the Horizon 2020 project RETALT, first subsonic retro propulsion experiments with oxygen/hydrogen combustion have been performed in the Hot Plume Testing Facility (HTPF) which consists of the Vertical Free Jet Facility Cologne (VMK) and an oxygen/hydrogen supply infrastructure. Oxidizer fuel ratios of around 0.7 were tested at Mach numbers of 0.6, 0.7, 0.8 and 0.9. The stagnation pressures in the model were around 21 bar. The steady and unsteady flow field features were analysed with regular video recordings, schlieren and infrared recordings. Furthermore, the pressures and temperatures in the base area were evaluated. The tests are compared to earlier cold gas tests of the same configuration. The steady flow field features are similar to those in cold gas test. However, the unsteady features prove to be very different. A general tendency of the dependence of the plume length on the momentum flux ratio, found in could gas tests, can be confirmed. However, the plume length is larger in the hot tests. The dominant frequencies found in cold gas tests in the modes of the Schlieren recordings differ from those found in the hot gas tests. Due to current trends in the European launcher designs towards the use of oxygen/methane engines, in the future, methane experiments are foreseen and an improved model concept shall enable higher oxidizer fuel ratios and, therefore, a better similarity to the flight conditions.